An image sensor is a semiconductor device for converting an optical image into an electrical signal. The image sensor is mainly classified as a charge coupled device (CCD) or a complementary metal oxide silicon (CMOS) image sensor.
The CMOS image sensor includes a photodiode and a MOS transistor in each unit pixel, and sequentially detects the electric signals of each unit pixel through a switching scheme to display an image.
Among the conventional image sensors, a 3-T type image sensor includes one photodiode area and three transistors, that is, a reset transistor, a drive transistor and a select transistor.
According to the related art, contacts are formed at predetermined portions of the photodiode area and at the drive transistor such that the photodiode area can be electrically connected to the drive transistor by means of metal filled in the contacts.
However, according to the related art, an etching process must be performed to form the contact in the photodiode area. Such an etching process may exert an influence upon the crystal structure of the photodiode area, thereby causing noise such as dark defects.
In addition, according to the related art, the contact and metal are provided at an upper portion of the photodiode area, so that light incident into the photodiode area may be interfered with by the contact and metal, lowering the photo-electronic effect. In addition, such a contact and metal may selectively block light incident into the photodiode area from the transistor area, causing image variation when the image is outputted.